Wiring for XLR input on unbalanced amp - diyAudio
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Old 16th April 2007, 03:13 AM   #1
Arx is offline Arx  Canada
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Default Wiring for XLR input on unbalanced amp

I'm building a fairly standard chipamp, but am using xlr connectors for inputs.

I haven't got the chip wired in a balanced topology, so what I'm wondering is which pins of the input I should wire to where?
Should I short the inverting input to ground, or would this create problems if I were to plug in a balanced preamp?

-Nick
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Old 16th April 2007, 04:32 AM   #2
BWRX is offline BWRX  United States
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Hi Nick.

The best solution would be to build a differential configuration if you only plan on using balanced sources. Or you can build a differential buffer and make an instrumentation amp. Or you can transformer couple the balanced signal. If you don't want to do any of those then your best bet is to just use the noninverting and ground pins of the balanced signal. Make sure the XLR ground is grounded at the source. You can also wire in a ~600ohm resistor between the balanced outputs to provide it with a proper load. If you short either of the balanced outputs to ground you risk damaging them. Some sources can handle continuous shorts to ground but certainly not all of them are.
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Old 16th April 2007, 05:18 AM   #3
Arx is offline Arx  Canada
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Quote:
Originally posted by BWRX
Some sources can handle continuous shorts to ground but certainly not all of them are.
Ok, cool.. That was what I would have assumed. Chances are I'll never be hooking this up to a balanced source anyways. I was just curious if there was a good way to wire it so it would work with a balanced source.

Really I just used XLRs because I hate RCA connectors.


I just shorted pins 1 and 3 together. I'll just be sure to stick with unbalanced sources.

For now it's just running off of 3 mini-plug to dual xlr cables I made up.

Digital crossover in software. I can't wait to try it.

-Nick
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Old 16th April 2007, 06:57 AM   #4
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
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Hi,
read W.Jung, D.Self and copy Jensen pseudo balanced source.

Sites are worth reading in detail.

http://www.jensentransformers.com/an/an003.pdf
fig 2.4 lets you set up the power amp with an XLR input to the inverting (pin3) and non-inverting (pin2) inputs and the NFB ratio is set with the extra resistor (470r) to ground back at the source.

Note, that the capacitors in the source set the XLR input to DC blocked on both inputs. You can omit these caps at the power amp, but if you do, then any other balanced or pseudo balanced source must provide the same DC blocking or your chipamp will apply DC output offset and DC gain to the output. The electros can be bypassed with 100nF to 1uF of foil or metallised film.
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